// sibling-overlap.mjs — shared deterministic overlap core for the skill rubric.
//
// Extracted from detect-skill-lifecycle.mjs (Sesjon 15 / B2) so BOTH the B1
// detector and eval.mjs can use the same overlap mechanics without a circular
// import (detect already imports from eval.mjs; eval.mjs now needs the overlap
// core, so it lives here and both import it).
//
// Two deterministic signals, combined per skill pair:
//   (1) boundary-tension graph — operator-curated k1-trigger-prompts.json:
//       each out_of_domain entry is a sibling prompt tagged belongs_to=<skill>,
//       a hand-labelled "confusable neighbour". Symmetric counts = how much two
//       skills sit on each other's trigger boundary.
//   (2) df-weighted lexical trigger-surface overlap — shared content tokens
//       between two descriptions, each weighted 1/df so domain-common vocabulary
//       ("azure") contributes little and distinctive shared tokens contribute more.
// combined = boundaryTension + weightedScore.
//
// K10 (B2): perSkillSiblingOverlap maps the pairwise combined scores to a
// per-skill verdict — a skill's K10 is its worst sibling pair; it FAILS when
// that exceeds the rubric threshold. This is the bar B3 merge/sanitize rests on.
//
// Zero dependencies — pure functions only (no fs/path). Inputs are passed in.

// Operator-designated B1 focus boundary (Azure-deployment: build <-> operate).
export const FOCUS_PAIR = ['ms-ai-engineering', 'ms-ai-infrastructure'];

// K10 rubric threshold — a skill FAILS sibling-scope-non-overlap when its worst
// sibling pair's combined score is at or above this. Set in the natural
// distribution gap (7.42 -> 6.67) just below the operator-designated eng<->infra
// boundary, so exactly that pair is surfaced as the B3 merge/sanitize signal.
export const K10_OVERLAP_THRESHOLD = 7.0;

// Function words (no + en) of length >= 3. Tokens < 3 chars are dropped anyway,
// so this list only needs the longer connectives. Domain nouns are NOT here —
// df-weighting handles common domain vocabulary instead.
const STOPWORDS = new Set([
  'the', 'and', 'for', 'with', 'between', 'before', 'not', 'are', 'that', 'this',
  'into', 'over', 'per', 'use', 'used', 'when', 'which', 'how', 'via', 'from',
  'eller', 'som', 'til', 'med', 'mot', 'ved', 'for', 'har', 'kan', 'ikke', 'der',
  'det', 'den', 'ein', 'eit', 'sin',
  // description-format boilerplate (every skill ends with "Triggers on:")
  'triggers', 'trigger',
]);

/** Lowercase, split on non-alphanumeric, drop stopwords + tokens < 3 chars. */
export function tokenize(text) {
  return (text.toLowerCase().match(/[a-z0-9æøå]+/g) || [])
    .filter((w) => w.length >= 3 && !STOPWORDS.has(w));
}

/** Trigger surface of a description: quoted phrases + content-token set. */
export function extractTriggerSurface(description) {
  const phrases = (description.match(/"([^"]+)"/g) || []).map((p) => p.slice(1, -1));
  return { phrases, tokens: new Set(tokenize(description)) };
}

/** token -> number of skill-surfaces that contain it. */
export function buildDocumentFrequency(surfaces) {
  const df = new Map();
  for (const s of surfaces) {
    for (const t of s.tokens) df.set(t, (df.get(t) || 0) + 1);
  }
  return df;
}

/** Order-independent pair key. */
export function pairKey(a, b) {
  return [a, b].sort().join('|');
}

/** Lexical overlap between two surfaces, df-weighted. */
export function lexicalOverlap(surfaceA, surfaceB, df) {
  const shared = [];
  for (const t of surfaceA.tokens) if (surfaceB.tokens.has(t)) shared.push(t);
  shared.sort();
  const union = new Set([...surfaceA.tokens, ...surfaceB.tokens]).size;
  const jaccard = union > 0 ? shared.length / union : 0;
  let weightedScore = 0;
  for (const t of shared) weightedScore += 1 / (df.get(t) || 1);
  return {
    shared,
    jaccard: Number(jaccard.toFixed(4)),
    weightedScore: Number(weightedScore.toFixed(4)),
  };
}

/**
 * Symmetric boundary-tension matrix from the curated prompt set.
 * Counts out_of_domain entries whose belongs_to is one of the real skills
 * (controls / out-of-stack entries are ignored). Keyed by pairKey.
 */
export function boundaryTensionMatrix(promptSet) {
  const skills = Object.keys(promptSet).filter((k) => k !== '_meta');
  const skillSet = new Set(skills);
  const m = {};
  for (const s of skills) {
    for (const e of promptSet[s].out_of_domain || []) {
      const b = e && e.belongs_to;
      if (!skillSet.has(b) || b === s) continue;
      const k = pairKey(s, b);
      m[k] = (m[k] || 0) + 1;
    }
  }
  return m;
}

/**
 * Pure core: given { skill -> description } and the curated prompt set, compute
 * the overlap report section. combined = boundaryTension + weightedScore
 * (operator-grounded primary signal + distinctive-lexical corroboration).
 */
export function computeOverlapFromInputs(descriptionsBySkill, promptSet) {
  const skills = Object.keys(descriptionsBySkill).sort();
  const surfaces = {};
  for (const s of skills) surfaces[s] = extractTriggerSurface(descriptionsBySkill[s]);
  const df = buildDocumentFrequency(Object.values(surfaces));
  const tension = boundaryTensionMatrix(promptSet);

  const pairs = [];
  for (let i = 0; i < skills.length; i++) {
    for (let j = i + 1; j < skills.length; j++) {
      const a = skills[i];
      const b = skills[j];
      const key = pairKey(a, b);
      const lexical = lexicalOverlap(surfaces[a], surfaces[b], df);
      const boundaryTension = tension[key] || 0;
      const combined = Number((boundaryTension + lexical.weightedScore).toFixed(4));
      pairs.push({ pair: [a, b], key, boundaryTension, lexical, combined });
    }
  }
  // sort by combined desc, then key asc for stable ties
  pairs.sort((x, y) => y.combined - x.combined || x.key.localeCompare(y.key));

  const focusKey = pairKey(...FOCUS_PAIR);
  const focusPair = pairs.find((p) => p.key === focusKey) || null;

  return {
    method:
      'deterministic: (1) operator-curated boundary-tension (k1-trigger-prompts belongs_to), ' +
      '(2) df-weighted lexical trigger-surface overlap. combined = boundaryTension + weightedScore.',
    focusPairReason:
      'Azure-deployment boundary engineering(build) <-> infrastructure(operate) — operator-designated B1 target.',
    pairs,
    focusPair,
  };
}

/**
 * K10 — sibling-scope-non-overlap, per skill.
 *
 * Maps the pairwise `combined` scores (from computeOverlapFromInputs) to a
 * per-skill verdict: a skill's K10 is its WORST sibling pair (max combined among
 * pairs containing it). pass = maxCombined < threshold. A failing skill is a
 * B3 merge/sanitize candidate against its worst sibling — never a blocker here.
 *
 * @param {Array<{pair:string[], combined:number}>} pairs  from computeOverlapFromInputs
 * @param {{threshold?:number}} [opts]
 * @returns {Record<string,{maxCombined:number, worstSibling:string|null, pass:boolean, threshold:number}>}
 */
export function perSkillSiblingOverlap(pairs, { threshold = K10_OVERLAP_THRESHOLD } = {}) {
  const out = {};
  const ensure = (s) => {
    if (!out[s]) out[s] = { maxCombined: 0, worstSibling: null, pass: true, threshold };
  };
  for (const p of pairs) {
    const [a, b] = p.pair;
    ensure(a);
    ensure(b);
    if (p.combined > out[a].maxCombined) {
      out[a].maxCombined = p.combined;
      out[a].worstSibling = b;
    }
    if (p.combined > out[b].maxCombined) {
      out[b].maxCombined = p.combined;
      out[b].worstSibling = a;
    }
  }
  for (const s of Object.keys(out)) out[s].pass = out[s].maxCombined < threshold;
  return out;
}